1. Field of the Invention
The present invention relates to an optical scanning device and a scanning type image display apparatus using the same, and in particular, it projects and displays a two-dimensional image on a scanning surface, for example, a screen surface by two-dimensionally scanning a light by a scanning device.
2. Description of the Related Art
A variety of optical scanning devices have been proposed, in which a spot (beam spot) of the light beam emitted from a light source is two-dimensionally optically scanned on a scanning surface, and by the residual image effect, a two-dimensional image is formed (for example, see Japanese Patent Application Laid-Open Nos. 2001-281583 and H11-84291)
In the optical scanning device, as means to scan the light beam from the light source, a polygon mirror, a galvanic mirror, a MEMS device prepared by a MEMS (Micro Electron Mechanical Systems) technology, and the like have been used.
In case the scanning device with sine-wave drive such as the galvanic mirror, the MEMS device, and the like is used, there has been generally known that a speed to optical-scan on the scanning surface becomes slow on the periphery.
Further, there has been generally known that when the optical scan is two-dimensionally performed by using such a scanning device, a scanning distortion is generated on the two-dimensional image formed on the scanning surface.
To display the two-dimensional image in high quality, it is necessary to suitably correct the scanning distortion.
A scanning optical system (image forming optical system) disclosed in Japanese Patent Application Laid-Open No. 2001-281583 includes an optical member having at least two reflecting surfaces including a rotational asymmetrical surface. The surface on the nearest side to the scanning surface from among the surfaces having optical power of the optical member has transmission action only.
By using this scanning optical system, an attempt is made to miniaturize the optical system by folding effect. Further, by having used the reflecting surface having optical power, though coma astigmatism due to decentering, and the like are generated, this decentration aberration is corrected by a rotational asymmetrical surface shape. Further, in case the polygon mirror is used as the scanning device, the scanning optical system is allowed to have an fθ characteristic, and in case the scanning device with sine-wave drive such as the galvanic mirror and the like is used, the scanning optical system is allowed to have an f arcsine θ characteristic. In this manner, the beam spot is constant-speed scanned on the surface to be scanned.
In the optical scanning device disclosed in Japanese Patent Application Laid-Open No. 2001-281583, when an attempt is made to secure both of a two-dimensional translatory scanning property and a constant speed scanning property by the optical characteristic of the scanning optical system, the optical system becomes complicated and large-sized. Hence, in Japanese Patent Application Laid-Open No. 2001-281583, the translatory scanning property is secured by the optical characteristic of the scanning optical system, and the constant speed scanning property is secured by electrical correction.
In this manner, in case the constant speed scanning property is secured by electrical correction, the intervals of pixels become unequal, and therefore, a control of newly prescribing pixel timing is required. Further, the number of clocks is required several times larger than ordinarily required or more, and a load applied on the electrical circuit is increased.
Further, since light quantity distribution on the scanning surface is in a relationship of inversely proportional to the optical scanning speed, unevenness in light quantity is generated so as to degrade the appearance quality of the image.